U.S. patent number 5,993,292 [Application Number 09/036,944] was granted by the patent office on 1999-11-30 for production of notchless wafer.
This patent grant is currently assigned to Super Silicon Crystal Research Institute Corp.. Invention is credited to Keiichiro Asakawa, Hiroshi Oishi.
United States Patent |
5,993,292 |
Oishi , et al. |
November 30, 1999 |
Production of notchless wafer
Abstract
A shallow notch 1 as a tentative mark is engraved on a periphery
of an ingot at a position corresponding to a predetermined crystal
orientation in the step of grinding the periphery of the ingot.
After the ingot is sliced to wafers, a mark 2 for indication of a
crystal orientation is carved on a sliced wafer at a position
determined on the basis of the notch 1 by laser marking.
Thereafter, the wafer is chamfered to a round shape, and the notch
1 is removed by the chamfering. Since a part where the mark 2 shall
be carved is determined on the basis of the notch 1, the mark 2 is
efficiently carved on the wafer without the necessity of subjecting
each wafer to an X-ray analyzer.
Inventors: |
Oishi; Hiroshi (Annaka,
JP), Asakawa; Keiichiro (Annaka, JP) |
Assignee: |
Super Silicon Crystal Research
Institute Corp. (JP)
|
Family
ID: |
13014675 |
Appl.
No.: |
09/036,944 |
Filed: |
March 9, 1998 |
Foreign Application Priority Data
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|
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Mar 11, 1997 [JP] |
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9-055995 |
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Current U.S.
Class: |
451/41;
125/13.02; 451/54; 451/44; 451/70; 451/69; 257/E21.237;
257/E23.179 |
Current CPC
Class: |
H01L
21/02008 (20130101); H01L 23/544 (20130101); C30B
33/00 (20130101); H01L 2223/54493 (20130101); H01L
2924/0002 (20130101); H01L 2223/54406 (20130101); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
C30B
33/00 (20060101); H01L 23/544 (20060101); H01L
21/02 (20060101); H01L 21/304 (20060101); B28B
001/00 () |
Field of
Search: |
;451/41,44,54,57,67,69,70 ;125/13.02,13.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Morgan; Eileen P.
Attorney, Agent or Firm: Webb Ziesenheim Logsdon Orkin &
Hanson, P.C.
Claims
What is claimed is:
1. A method of producing a notchless wafer, comprising the steps
of:
engraving a notch extending along an axial direction of an ingot on
a periphery of said ingot at a position corresponding to a
predetermined crystal orientation during grinding a periphery of
said ingot;
slicing said ingot to wafers;
carving at least one laser mark for indication of a crystal
orientation on said wafer at a position determined on the basis of
said notch; and
chamfering said wafer to a round shape,
wherein said notch is engraved to a depth such that said notch is
removed by said chamfering.
2. The method according to claim 1, wherein another laser mark for
indication of identification of the wafer is carved on an edge of
the wafer at a position apart from the laser mark for indication of
crystal orientation.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing a
round-shape wafer on which a laser mark for indication of a crystal
orientation is put instead of a notch or orientation flat.
A wafer sliced off an ingot is processed in various steps such as
lapping, chamfering and etching. A mark for indication of a crystal
orientation is carved on an edge of the wafer used in these steps.
The mark is used for setting the wafer, when the wafer is scribed
along a cleavage plane for instance.
Such marks are put on wafers by various methods.
OF method is the most popular one by which an orientation flat is
formed at an edge of a wafer. The orientation flat is used for
specifying a crystal orientation of the wafer in the subsequent
processing steps. However, it is difficult to precisely align a
wafer using the orientation, since the orientation flat is formed
in a relatively broad area crossing an edge of the wafer at an
obtuse angle. Besides, the orientation flat puts restrictions on a
shape of an electrostatic chuck used for handling the wafer and
causes harmful effects on dynamic balance during spin rotation of
the wafer.
A notch engraved on an edge of a wafer is also used as a mark for
indication of a crystal orientation. In this case, a notched edge
shall be polished to specular glossiness, so as to distinctly
detect the notched part during measuring in the subsequent steps.
Engravement of the notch likely causes induction of residual
stresses at the notched part. Although residual stresses put
harmful influences on properties of the wafer, it is difficult to
completely remove residual stresses.
Notchless wafers having laser marks for indication of a crystal
orientation have been recently used in order to avoid these
problems. The laser mark is carved on a front or back side of a
wafer by partially melting a surface layer of the wafer with
irradiation of a laser beam.
In a conventional laser marking method, each wafer is tested by an
X-ray analyzer to detect a crystal orientation of the wafer, and a
mark for indication of crystal orientation is put on at a proper
position. A commonly used crystal orientation is <110>.+-.1
degree. This method requires a marking operation for each wafer,
resulting in poor productivity and heavy duty on the X-ray
analyzer.
SUMMARY OF THE INVENTION
The present invention aims at efficient production of a notchless
wafer without the necessity of testing each wafer for detecting a
crystal orientation.
According to the present invention, a shallow notch extending along
an axial direction of an ingot is engraved as a tentative mark for
indication of a crystal orientation on a periphery of the ingot at
a position corresponding to a predetermined crystal orientation in
a step of grinding the periphery of the ingot. After the ingot is
sliced to wafers, a mark for indication of the crystal orientation
is put on a sliced wafer at a position determined on the basis of
the notch. Thereafter, the sliced wafer is chamfered to a round
shape, and the notch is removed by the chamfering.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart for explaining the steps of producing a
notchless wafer according to the present invention.
FIG. 2 is a schematic view illustrating a device for manually
determining a position for carving a mark for indication of a
crystal orientation on a wafer
PREFERRED EMBODIMENT OF THE INVENTION
In the newly proposed method, a notch 1 extending along an axial
direction of an ingot is engraved on a periphery of the ingot at a
position indicating a predetermined crystal orientation, when the
ingot is ground at its periphery. The crystal orientation is
measured by the same X-ray analyzer as that used for production of
a notchless wafer in a conventional method.
Since the notch 1 will be removed in a chamfering step succeeding
to carving a mark for indication of a crystal orientation, the
notch 1 of 0.2-0.7 mm in depth is engraved on the periphery of the
ingot. The notch 1 is as approximately a third shallow as a
conventional notch for indication of a crystal orientation, so that
the notch 1 can be easily engraved by slight grooving.
After the notch 1 is engraved on the periphery of the ingot, the
ingot is sliced to wafers having a predetermined thickness by an
inner diameter saw, a wire saw or the like.
Thereafter, a mark 2 for indication of a crystal orientation is
carved on the sliced wafer using a hard laser marking device which
outputs high energy laser beams. A position to be carved by the
laser marking is determined on the basis of the notch 1 without
necessity of subjecting every one wafer to an X-ray analyzer as in
a conventional method.
The mark 2 for indication of a crystal orientation is carved in
such depth that the mark 2 of 10 .mu.m or deeper will remain in a
finished wafer. Such depth of the mark 2 is easily controlled by
adjustment of a laser power.
Other marks for indication of specification, identification,
production number, user need, etc. may be carved by the same way in
addition to the mark 2 for indication of a crystal orientation.
These marks may be put on as a bar code at a position apart from
the mark 2 for indication of a crystal orientation so as to
distinguish them from the mark 2.
In order to automate the laser marking, a position of the notch 1
is detected by a video camera and an image processor, and a part
where the mark 2 shall be carved is calculated from the detection
result.
A device shown in FIG. 2 is used in case of manually determining a
position for carving the mark 2. The device has rollers 4 for
supporting a wafer 3 at one side. A notch pin 6 is pressed onto the
opposite side of the wafer 3 by a spring 5. When the wafer 3 is
in-plane rotated, the notch 1 moves along a peripheral direction
and accepts the notch pin 6. As a result, the wafer 3 is fixed, and
a position where the mark 2 shall be carved is specified.
After the mark 2 is carved on the wafer 3, the wafer 3 is chamfered
to a round shape. The notch 1 is removed by the chamfering. Hereon,
the notch 1 can be easily removed by slight chamfering, since the
notch 1 is shallow compared with a notch engraved as a mark for
indication of a crystal orientation in a conventional method.
The round wafer 3 is then lapped, polished and finished to a final
product.
As mentioned above, a position where the mark 2 for indication of a
crystal orientation shall be carved is determined on the basis of
the notch 1, so that the mark 2 is efficiently put on the wafer 3
by laser marking without the necessity of subjecting each wafer to
an X-ray analyzer as in a conventional method.
EXAMPLE
When a periphery of an ingot of 200 mm in diameter was ground, a
notch 1 of 0.5 mm in depth extending along an axial direction of
the ingot was engraved on the periphery of the ingot. The ingot was
then sliced to wafers of 0.9 mm in average thickness by a wire
saw.
A mark 2 for indication of a crystal orientation was carved at a
depth of 0.09 mm on an edge of the wafer 3 at a position opposite
to the notch 1 by a hard laser marking device with a laser power of
50 W. The edge of the wafer was then chamfered by 1.2 mm in
diameter. The notch 1 was removed by this chamfering, and the wafer
3 was reformed to a round-shape 7 of 200 mm in diameter.
After the round-shape wafer 7 was lapped, polished and finished to
a final state, depth of the mark 2 was 0.01 mm. Although the mark 2
became relatively shallower by these processes, the mark 2 of such
depth was effective for detection of a crystal orientation.
According to the present invention as aforementioned, a shallow
notch is engraved on a periphery of an ingot, the ingot is sliced
to wafers, and then a mark for indication of a crystal orientation
is carved on the sliced wafer by laser marking. Thereafter, the
marked wafer is chamfered to a round shape, and the notch is
removed by the chamfering.
Since a position where the mark shall be carved is determined on
the basis of the notch, notchless wafers are efficiently produced
without the necessity of subjecting each wafer to an X-ray analyzer
as in a conventional. The marked wafer obtained in this way has
improved handling ability in the subsequent steps due to its round
shape.
* * * * *